- Anticlimax Boss: Once you find out how to damage Z-Leo, you'll find him much easier than many of the other bosses (such as Seven Force and Epsilon-1), since his only move for most of the fight besides the reflectable fireballs is his telegraphed, predictable Arm Cannon. His laser attack is tougher to dodge, but he only starts using it after hitting half health.
- Awesome Music: The whole soundtrack; of worthy note is "Runner AD2025", the first stage theme.
- Best Boss Ever: Seven Force is just as cool, varied, and difficult as it was in Gunstar Heroes, putting up a greater fight than even the final boss.
- Big-Lipped Alligator Moment: A blue teddy bear, menaced by kissing aliens, operates a power boat and is unceremoniously thrown overboard by a giant lobster. Hell, half the bosses are like this; a cyborg wolf with an Arm Cannon riding a horse, anyone?
- Breather Boss: Melon Bread, a.k.a. "Jampan", is just as easy as he was in Gunstar Heroes, and you can, as before, kill him before he can even attack. Right after him is Seven Force.
- Even Better Sequel: Even Better Spiritual Successor in this case. While Gunstar Heroes is a classic Treasure masterpiece even to this day, this game refines the combat, is faster and even more intense, provides greater challenge and reward in equal measure, has even better music, and gets rid of some of the more awkward gameplay changes and the occasional bits that didn't work.
- Game-Breaker: The Phoenix Force attack, which is only usable at full life and consumes a small portion of it afterwards, inflicts a hit of damage on enemies and bosses for every single frame of contact it makes. With the right set-up and some luck, it's possible to destroy many bosses in a single shot of it.
- Goddamned Bats: Those bee-like enemies that you fight between boss battles. Better have Homing Force ready, as they come in swarms, shoot at you, then fly erratically and kamikaze you. The bomb-dropping alien birds also get really annoying.
- Goddamned Boss: Artemis Force. It only attacks by jumping forward and firing explosive shots, which can be dashed past easily, but it's invincible everywhere except the back, and unless you're attacking the difficult-to-hit tailtip, you will only deal five percent damage to it. Trying to kill this form normally just wastes a lot of weapon energy. There's an alternate strategy in parrying the explosive shots to gain health and using the Phoenix Force, but parrying the shots is difficult to do and Artemis Force likes to spend long stretches of time without using the attack. It's like Artemis Force was intentionally designed to rob you of valuable time and/or ammo to kill Sirene Force.
- It's Hard, So It Sucks!: The first miniboss alone (fought around a minute into the game) is hard enough to drive people away from the game.
- Nightmare Fuel: More than a few of the enemies encountered are grotesque.
- Self-Imposed Challenge: During the initial weapon selection and configuration, the player has the option to make all information about his health, ammunition and boss health into "???", essentially preventing the player from tracking how much damage was taken or dealt or how much ammo they have left.
- Tear Jerker: That cute blue bear that drives the boat for you? He gets thrown into the river by the Lobster boss, helplessly calling for help.
- That One Attack: Epsilon-1's bombing wave, where it flies upwards, comes down in a random spot and fires straight down, and fires bullets from all of its wing segments while flying back offscreen. Epsilon-Eagle's dash won't help you dodge the initial fire since he'll just get caught in the wing bullets; you just have to quickly move out of the way and stay in the safe spots next to Epsilon-1's head.
- That One Boss:
- Seven Force is a five-phase battle, which is pretty daunting in a game that otherwise has one boss per stage with an occasional mini-boss. Each form has something to trip you up: Valkyrie Force's weakpoint is constantly blocked by its arms, Medusa Force heavily resists all weapons and takes a while to wear down unless you knock bombs into it, Silpheed Force is fought in freefall and covers up its weakpoint to stall the battle, and Artemis Force is a Goddamned Boss. The final form, Sirene Force, is the worst. You fight it underwater, depriving you of your fire-based weapons, in a constantly moving vortex full of mines, with a timer that's about to run out. You'll need a lot of Lancer Force ammo and precise aim to take it out before it wears you down.
- Epsilon-1, your character's Superpowered Evil Side which manifests itself in an evil giant robotic eagle bent on destroying humanity. Its weak spot, the head, is obscured by its two talons that absorb all shots they touch. Oh, and all of its attacks do 200 damage, enough to kill you in a few hits. Finally, the only weapon that does decent damage against it is the ammo-scarce Lancer Force (provided it doesn't get blocked by the talons), which may still need to recharge after three boss battles in a row against Sunset Sting, Viblack, and Back Stringer (making the longest stretch of gameplay with no level segment to regain health or ammo from). Fortunately, it's one of the few bosses that doesn't do Collision Damage to you.
YMMV / Alien Soldier